Recently, MIMO (Multi Input Multi Output) communication is attracting attention in wireless communication as a technique that makes it possible to improve spectral efficiency. In MIMO communication, a transmitting apparatus having a plurality of transmitting antennas transmits at the same time streams formed with a plurality of bits from the transmitting antennas, and a receiving apparatus having a plurality of receiving antennas demultiplexes the streams from the transmitting apparatus and demodulates the demultiplexed streams. Therefore, when mutually different streams are transmitted at the same time from all transmitting antennas of the transmitting apparatus, it is theoretically possible to improve spectral efficiency by equivalent times to the number of the transmitting antennas compared to a case where only one transmitting antenna is used.
Furthermore, as disclosed in Patent Document 1, by providing differences in transmission power among the transmitting antennas, transmitting streams formed with bits having the high degree of importance from transmitting antennas having high transmission power and transmitting streams formed with bits having the low degree of importance from transmitting antennas having low transmission power, it is possible to improve the overall packet error rate (PER) performance in MIMO communication.
Moreover, Patent Document 1 discloses that, when a retransmission request is fed back from the receiving apparatus, the transmitting apparatus transmits streams from transmitting antennas different from the last transmission. By this means, it is possible to reduce the possibility that only specific streams may include errors consecutively and reduce the number of retransmissions.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-72427